You can play one of our usual sounds with: play -q /opt/het/hetdex/etc/sounds/alert-1.ogg

Sometimes the speaker output level is turned down, either on the speaker under the left-most screen or in the computer volume settings. 
There might be a small icon in the top bar on the screen.
When you put the cursor on it, a pop-up screen reports something like:
    Output: 8%
At the bottom of this screen:   Internal Audio Analog Stero
If you click the icon, a slide bar opens up and you should push it to 100%.
At this point you might hear the sound when we run the play command above.

You can also use the volume adjustment buttons on the keyboard